Add extra information to FormatException.

pkg/json_rpc_2/test/server/parameters_test.dart

Index: pkg/json_rpc_2/test/server/parameters_test.dart
diff --git a/pkg/json_rpc_2/test/server/parameters_test.dart b/pkg/json_rpc_2/test/server/parameters_test.dart
index 64fe23260e75899dc13b6e2c2dd50b7a650e58d0..3de03598c93731f48f8148f7c373619362fe7b9a 100644
--- a/pkg/json_rpc_2/test/server/parameters_test.dart
+++ b/pkg/json_rpc_2/test/server/parameters_test.dart
@@ -229,7 +229,8 @@ void main() {
     test("[].asDateTime fails for invalid date/times", () {
       expect(() => parameters['string'].asDateTime,
           throwsInvalidParams('Parameter "string" for method "foo" must be a '
-              'valid date/time, but was "zap".'));
+              'valid date/time, but was "zap".\n'
+              'Invalid date format'));
     });
 
     test("[].asUri returns URI parameters", () {
@@ -262,9 +263,7 @@ void main() {
       expect(() => parameters['invalid-uri'].asUri,
           throwsInvalidParams('Parameter "invalid-uri" for method "foo" must '
               'be a valid URI, but was "http://[::1".\n'
-              'Missing end `]` to match `[` in host at position 7.\n'
-              'http://[::1\n'
-              '       ^'));
+              'Missing end `]` to match `[` in host'));
     });
 
     group("with a nested parameter map", () {